There are many organopolysiloxane compositions which are readily curable to give elastomeric rubbers. There are also many cure systems for such organopolysiloxane compositions and lengthy discussions on such systems are not required because they are well known to those skilled in the art.
Examples of some of the better-known techniques are for instance exposing an acyloxy end-blocked polydimethylsiloxane to moisture or contacting a hydroxy end-blocked, linear polydimethylsiloxane with ethylpolysilicate or alkyltrialkoxysilanes as crosslinking agents. Cures are also effected by heating polysiloxanes, containing unsaturated organic groups, in the presence of peroxides. Also, cured rubbers are obtained by contacting polysiloxanes containing unsaturated organic groups with polysiloxanes containing silicon bonded hydrogen, in the presence of platinum or rhodium as catalysts.
The present invention deals, in part, with the latter cure system.
One of the things that all of these cure systems have in common is their inability to adhere properly on the substrates they are being used on.
In this regard, the acyloxysiloxanes, or the use of acyloxysilanes as crosslinkers sometimes enhances the self-adhering properties of such curable organopolysiloxane systems but they too have problems on certain substrates.
Of all of the cure systems noted above, the one which requires the most assistance in bonding to various substrates is the system which cures through addition of silicon bonded hydrogen to unsaturated organic groups on silicon. This problem is especially apparent when such systems are used on silicones as the substrate, that is, when curing silicone elastomeric materials on silicone substrates.
On the other hand, those skilled in the art desire very much to use the silicon bonded hydrogen addition to unsaturated organic groups on silicon cure system because it has many desirable features such as rapid cure, no or essentially no, by-products of the cure reaction, less toxicity than the other cure systems, greater shelf stability, etc.
Further, there are not the disadvantages associated with self-adhering materials that there are with those systems which have to be primed.
For example, the use of a primer to adhere elastomers to substrates requires an additional preparatory step wherein the substrate must be treated with the primer before the curable material is put in place.
Aside from the obvious disadvantage of having an extra step in the placement and use of such curable elastomers, the general use of primers per se has some disadvantages such as the time lapse required for the primer to dry and partially react on the substrate before the elastomer is applied; the inability to cover the entire surface of irregularly shaped or intricately shaped substrates and, the inability of the primer itself to give uniform and sufficient adhesion to the elastomer.
Self-adhering organopolysiloxane compositions which utilize the silicon bonded hydrogen addition to silicon bonded unsaturated organic groups as the cure system have been attempted.
In U.S. Pat. No. 3,527,655, self adhering organopolysiloxanes were prepared, by adding to the curable organopolysiloxane, a separate organopolysiloxane which was a cohydrolyzate of vinyl trichlorosilane and vinyl triethoxysilane.
The disadvantages of such a self-adhering system, however, were the inability of the material to adhere to variable substrates and it's inability to adhere to most plastics.
It is therefore an object of this invention to produce organopolysiloxane compositions, which are curable through the silicon bonded hydrogen addition to unsaturated organic groups on silicon, which have enhanced adhesion to various substrates.
It is a further object of this invention to produce organopolysiloxane compositions, which are curable through the addition of silicon bonded hydrogen to unsaturated organic groups on silicon, which have especially good adhesion to silicone substrates.